1. Field of the Invention
This invention relates to a process for refining a raw sugar, particularly raw sugar from the sugar cane sugar industry.
2. Description of Art
Such known processes comprise first a refining of the raw sugar which usually consists in washing the latter with the run-off of the last crystallisation of high-grade products which dissolves the surface film of crystals which is the most charged with coloring agents. A refined sugar and a refining run-off generally containing approximately 80-85% by weight of dry matter, which is essentially composed of sugar, are thus obtained. Said run-off is then subjected to several crystallisations in the low-grade product line to obtain a raw sugar (which will be remelted with the refined sugar) and molasses. Since the concentrated refining run-off has a high coloring agent content, the crystallisation operations require very long crystallisation times and consequently make the crystallisation equipment unavailable for other operations during an appreciable period. As concerns the refined sugar (high-grade products), it is subjected to an additional purification comprising the steps of remelting, carbonatation (treatment using calcium oxide or lime milk and carbon dioxide) or phosphatation (treatment using calcium oxide or lime milk and phosphoric acid), front filtration or clarification, decolorization and crystallisation.
It thus will be seen that, in the aggregate, these known processes are unsatisfactory economically, essentially because of the tedious nature and high cost of the refining run-off crystallisation operations and production of low-grade products (raw sugar and colored molasses) at the end of said run-off purification.